The process of re - creating original modulating frequencies from the carrier is referred to as DEMODULATION or DETECTION. The circuit in which restoration is achieved is called the DETECTOR or DEMODULATOR. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. The output of an ideal detector must be an exact reproduction of the modulation existing on the wave. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. A nonlinear device is required for demodulation. This nonlinear device is required to recover the modulating frequencies from the envelope.There are several ways of demodulation depending on how parameters of the base - band signal are transmitted such as amplitude, Frequency or Phase.

Peak detection : is one of the most important time - domain functions performed in signal monitoring. Peak detection is the process of finding the locations and amplitudes of local maxima and minima in a signal that satisfies certain properties. These properties can be simple or complex. For example, requiring that a peak exceeds a certain threshold value is a simple property. However, requiring that a peak's shape resembles that of a prototype peak is a complex property.
A peak detector is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal. An AC voltage source applied to the peak detector, charges the capacitor to the peak of the input. The diode conducts positive "half cycles," charging the capacitor to the waveform peak. When the input waveform falls below the DC "peak" stored on the capacitor, the diode is reverse biased, blocking current flow from capacitor back to the source.